Retroreflective highway sign manufacture is relatively labor intensive and causes certain environmental concerns. Moreover, such signs are frequent targets of "spray can" vandalism. Present signs also "black out" under certain climatic conditions. The present invention presents a unique approach to the efficient manufacture of preprinted signs allowing for their more efficient and economic manufacture; the method enables the reduction of some environmental problems encountered at sign shops, and permits the manufacture of retroreflective highway signs which are more vandal resistant and less subject to black outs.
U.S. Pat. Nos. 4,601,861 and 4,618,518, assigned to Applicants' assignee, both disclose retroreflective sheeting and method and apparatus for embossing a precision optical pattern in a resinous sheet or laminate. In particular, those patents relate to cube corner type retroreflective sheeting having particular use in making highway signs, street signs and the like. Both of those patents are incorporated herein by reference in their entirety. The present invention is a significant improvement of the sheeting produced generally in accordance with such patents.
Currently highway signs generally are made in sign shops, which receive rolls containing continous sheets of previously produced retroreflective material. The rolls generally contain some form of adhesive backing protected by a release liner. In order to prepare the signs, the release liner is removed to expose an adhesive backing which allows the retroreflective sheeting to be applied to the sign substrate. Excess sheeting overhanging the sign substrate is then trimmed off.
A legend of any desired color or shape is then printed on the front face of the sheeting that is mounted on the sign substrate. The paint or ink used for printing the legend must permanently adhere to the surface and thus the outer or front surface of the reflective sheeting requires a material having an affinity for paint. (For purposes hereof, the term "paint" or "printed" will encompass any material such as inks, paints or the like used by sign shops to apply the desired final legend to the sign.) The paint is allowed to dry, generally for 24 hours, and then an overlay of clear coating is applied and allowed to dry for another 24 hours, to form the completed sign.
Being the normal method used in the industry to produce road signs, the surface of the sheeting can be seriously damaged when exposed to vandalism. If the vandals spray paint on the sign face, the paint is difficult, if not impossible, to remove, because the retroreflective material itself has an affinity for paint. Strong solvents cannot be used because they would destroy the legend on the sign's front face.
Another significant disadvantage is that the painting of the legend, and the drying steps, both labor intensive, must take place in the sign shop. However, the volatile type materials used in the printing and finishing of the signs and in their curing, produce environmentally objectionable waste materials and vapors. Even the towels and rags used for cleaning purposes during the printing and coating operations, increasingly are more difficult to dispose of in compliance with various state and federal environmental regulations.
The present invention materially overcomes both the labor intensive aspects at the sign shops, in which the printing and coating steps each may take 24 hours of drying time. It also may significantly eliminate the use of some environmentally objectionable materials.
Another problem with prior art signs, is that under certain climatic conditions dew, or water beads, form on the sign's front surface. The dew, by distorting the incoming and outgoing light rays, effectively diminishes the retroreflective capability of the sign, thus rendering the sign, its background and perhaps the legend, totally non-retroreflective. This condition often is referred to as a "dew-out".
The present invention overcomes the disadvantages of the prior art by providing a retroreflective material which, when formed, has the particular sign legend formed below the outer surface and prior to being embossed, with the coating, adhesive and back cover or release liner added thereafter to form the completed laminate.
It is a primary object of the present invention to provide a unitary reflective material for use in sign making which has the legend of desired shape and color printed on a surface of a resinous material that is then covered by an ultraviolet absorbent overlay that has a poor affinity for paint to protect the sign from not only the sunlight but also from permanent damage due to external events such as painting by vandals.
A significant advantage of the pre-printed signs formed by the present invention is that, because the outer layer is not restricted to materials that accept printing inks, not only can the new sign be made both vandal and solvent resistant, but by the proper selection of the front surface resin to include one having a low surface energy minimizing water beads, the "dew out" condition frequently observed in existing signs may be minimized so the loss of retroreflectivity attributed to the dew may be significantly reduced.
The term "legend" as used herein means any particular combination of words and/or symbols and/or colors intended to convey some message--such as "Stop"; "Yield" or any other instruction or warning.
In the present invention, a sheet of resinous material, which may be a thermoplastic type of material such as acrylic, has printed thereon the desired legend with a paint formulated to meet the color requirements and which remains stable through the heat of processing. An ultraviolet absorbing overlay is bonded by laminating it to the surface of the resinous material having the legend thereon to protect the legend from the deleterious effect of weathering. The ultraviolet absorbing overlay preferably also is a material having a poor affinity for paint and thus, in the final product, can be cleaned if marred by vandals; it also will be dew resistant.
The present invention, by employing such embossing processes and apparatus provides an efficient and economical method of forming rolls of retroreflective materials containing a succession of preprinted legends thereon.
In the preferred form, after the preprinted material has been passed through the embossing machine, it may be passed through the other stages described in the prior art patents, where a layer of hydrophobic granular silica material is applied to the embossed side of the resinous sheeting material to provide a cell pattern and to enhance the daytime whiteness of the product. A protective back coating is then applied to the silica and exposed rear surfaces to form a smooth surface; adhesive is then applied to the coating. A removable release liner is applied to the adhesive to prevent accidental contact with the adhesive and to allow winding and further handling.
With the present invention, a roll of the sheeting material is then sent to the sign shop where it may be simply unwound using standard equipment in the industry, which removes the release sheet and applies the retroreflective material to a prepared sign substrate. Excess material is then trimmed and the sign is completed. There is no printing nor curing required.
Thus, it is an object of the present invention to provide a method of making a retroreflective material for use in signs wherein a desired legend is printed on one surface of a resinous sheeting material and which is covered by an ultraviolet (UV) absorbent overlay to reduce damage to the legend by sunlight. The overlay, also having a poor affinity for paint, allows the sign to be cleaned in the case of damage such as by vandals applying paint thereto.
In summary, the present invention achieves four significant advantages: First, the preprinted signs, having the UV absorbing material on the outer surface with the printed legend below that surface, gives certain sign processing advantages and longer life, while effectively reducing the labor intensive aspects of producing the sign. Second, the preprinted signs, being formed with a weatherable outer surface that has a poor affinity for paint, can be cleaned with a solvent which renders the sign more vandal resistant. Third, the outer surface material may be of a composition that provides low surface tension to inhibit water beading or "dew outs". Finally, the pre-printing may reduce some of the environmental problems presently associated with on site sign printing at numerous sign shops.